This invention relates to silver halide photographic materials and especially to photographic silver halide emulsions which can be advantageously used for silver complex diffusion transfer process and methods for producing same.
The theory of the silver complex diffusion transfer process (DTR process) is disclosed in U.S. Pat. No. 2,352,014 and is well known in other various patents and literatures.
In the DTR process, silver complex salts are transferred from a silver halide emulsion layer to an image receiving layer by diffusion and are converted to silver images mostly in the presence of physical development nuclei. For this purpose, the silver halide emulsion layer exposed imagewise is arranged in contact with an image receiving layer or brought into contact with an image receiving layer in the presence of a developing agent and a silver halide complexing agent to convert unexposed silver halide to a soluble silver complex salt.
The silver halide in the exposed areas of silver halide emulsion layer is developed to silver which can no longer be dissolved and so cannot be diffused.
On the other hand, the silver halide in the unexposed areas of the silver halide emulsion layer is converted to a soluble silver complex salt, which is transferred to an image receiving layer where it forms a silver image, ordinarily, in the presence of development nuclei.
These actions of the exposed and unexposed areas are opposite in direct-positive silver halide emulsions. The DTR process has wide uses such as for reproduction of documents, production of lithographic printing plates, production of block copying materials, instantaneous photographs, etc.
As mentioned above, processing according to the DTR process is carried out in the presence of silver halide complexing agents and developing agents.
Silver halide complexing agents which are suitable for use are well known and, for example, there are (1) thiosulfates, (2) thiocyanates, (3) aminethiosulfate anhydride disclosed in U.S. Pat. No. 3,169,962 and (4) cyclic imide compounds disclosed in U.S. Pat. No. 2,857,276. Moreover, it is known that mercapto compounds are good silver halide complexing agents and, for example, Japanese Patent Publication (Kokoku) No. 11957/71 discloses use of various kinds of mercapto compounds in a combined developing and fixing composition.
The complexing agents are mainly incorporated into processing solutions or image receiving elements.
However, although it is depending on the kind of these complexing agents, in alkaline processing solutions, they decompose or react with other compound, e.g., developing agents, to lose complexing action, or their complexing ability decreases during storage of the processing solution or running processing. Therefore, it is preferred, if possible, to incorporate the complexing agents in photographic materials.
For example, the inventors proposed in Japanese patent application No. 84743/79 that lithographic printing plates extremely excellent in ink receptivity can be obtained by incorporating 2-mercaptobenzoic acid which is one of the mercapto compounds described in said Japanese Patent Publication (Kokoku) No. 11957/71 in constituting layers of lithographic printing plates obtained by using DTR process. However, it has been found by the subsequent researchers that even if the mercapto complexing agents for silver are incorporated in layers which are not light sensitive as well as silver halide emulsion layers, there occur problems such as desensitization and softening in tone which are promoted when the photographic materials are stored.
As a result of the inventors' intensive research in an attempt to improve said defects, it has been found that unexpectedly the best results are obtained by incorporating mercapto complexing agents for silver salts in silver halide emulsions at the time of their preparation and said defects can be completely overcome.